Heat exchange fluids

ABSTRACT

Carboxylate salts of amines are used as components of heat exchange fluids. The amines may have a ratio of N to C of 1:0 to 1:12 and the carboxylate anion may be derived from an acid of the formula H(CH 2 ) 0-3 COOH. A preferred monoamine heat exchange fluid utilizes triethanolamine formate. Lower carboxylate salts of diamines and triamines having the formula R 2 [N[(CH 2 ) m NR] 1-2 ]R where each R is independently selected from moieties of the formula —C n H 2n+1  and moieties of the formula H[O(CH 2 ) 1-4 ]—, each m is independently a number from 1 to 6, and each n is a number from 1 to 4, are disclosed as compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/141,390, filed May 8, 2002, now U.S. Pat. No. 7,060,198 which patentapplication is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aqueous solutions of amine carboxylates, preferably triethanolamineformate, are used as heat exchange fluids.

2. Description of the Related Art

Fluids used for heat exchange in many contexts suffer from the fact thatthey are either inefficient or environmentally questionable. There is aneed for new heat exchange fluids that are environmentally acceptable aswell as efficient.

SUMMARY OF THE INVENTION

The present invention comprises the use of solutions of aminecarboxylates as heat exchange fluids. Useful compositions combine aminesof the formula R¹R²R³N with carboxylic acids of the formulaH(CH₂)₀₋₂COOH, preferably in equimolar ratios, where R¹, R², and R³ areindependently selected from moieties of the formula C_(n)H_(2n+1) andmoieties of the formula H[O(CH₂)₁₋₄]—, where n is an integer from 0 to4. Since the compositions will be in aqueous solution, it is useful toexpress them in the dissolved form. For example, our preferred compound,triethanolamine formate, comprises the reaction product of molarequivalents of triethanolamine and formic acid, and has the formula(HOCH₂CH₂)₃NH⁺HCOO⁻ in water. To make it, the triethanolamine may beadded first to water; then formic acid is added slowly to control theexotherm from the neutralization between the acid and the amine.Neutralization is effected preferentially with respect to any possibleesterification which could occur between the carboxylic acid and anyhydroxyl groups present in the amine. The solution becomes transparentafter mixing for a few hours. More generally, where any of severalcarboxylic acids is used, the formulation in water may be expressedR₃N⁺H(CH₂)₀₋₃COO⁻, where each R is independently as defined above forR¹, R², and R³.

Definition: We use the term “triethanolamine formate” to mean any of (a)a mixture of 1 mole of triethanolamine (“TEA”) and one mole of formicacid, (b) a mixture of triethanolamine and formic acid in a molar ratioof 1:4 to 4:1, (c) a composition of the formula (HOCH₂CH₂)₃NH⁺HCOO⁻, or(d) a combination of (a) or (b) with (c) in a ratio up to 100:1. Similarreferences can be made to such compositions within the above generalformula as diethylamine acetate, monoethanolamine propionate, ammoniumformate, and trimethylamine formate.

We are not limited to the monoamines described above. Our inventionincludes the use of diamine carboxylates—for example, compounds of thegeneral formula R₂NCH₂CH₂NR₂ where each R is independently selected frommoieties of the formula C_(n)H_(2n+1) and moieties of the formulaH[O(CH₂)₁₋₄]—, where n is an integer from 0 to 4, are reacted with acarboxylic acid as described above for triethanolamine formate,preferably with the nitrogen and carboxylic groups being present inmolar equivalents. Such diamines are included (and are useful in ourinvention) in the general formula R₂N(CH₂)_(m)NR₂ where each R isdefined independently as stated above and m is an integer from 1 to 6.Moreover, we may use any triamine of the formulaR₂N(CH₂)_(m)NR(CH₂)_(m)NR₂, where each R is defined independently asstated above and each m is independently an integer from 1 to 6. In eachcase—that is, with reference to both diamines and triamines, at leastone of the amine nitrogens is associated with a carboxylate group having1-4 carbon atoms, as described above with reference to the monoamines[that is, H(CH₂)₀₋₃COO⁻]. Thus, we include such compounds astetrakishydroxyethylenediamine for association with at least onecarboxylate group of formic, acetic or propionic acid. Mixtures ofamines useful in our general formulas may be found in such materials asamine heads, the term applied to an unrefined mixture of alkyl diamineshaving about 4 to 6 carbon atoms, commercially available as a byproductof the manufacture of hexamethylene diamine and similar products. Suchmixtures commonly include various cyclic amines, which are also usefulin our invention. Any such mixtures may be reacted with the carboxylicacids described to obtain compositions useful in our invention. As ageneral principle, we may use any mono-, di-, or triamine, cyclic ornot, having an atomic ratio of N to C from 1:0 to 1:12 for combinationwith the carboxylate of the type described above. A general formula forthe amines, including ammonia, the monoamines, diamines and triamines,is R₂[N[(CH₂)_(m)NR]₀₋₂]R, where each R is independently as definedabove and each m is independently an integer from 1 to 6. At least oneof the nitrogens of such amines is associated with a carboxylate groupas explained above. Further, the amine may be additionally ethoxylated,propoxylated, or butoxylated to contain up to three additional alkoxygroups in each R. Examples of compounds within this general formulainclude ethylene diamine diformate, hexamethylene diamine diformate,hexamethylene diamine diacetate, tetrakis diethoxy hexamethylene diaminediformate, and tetrakis ethanol ethylene diamine dipropionate. Anexample of a triamine derivative is [HO(CH₂)₂O(CH₂)₂]₂N(CH₂)₂NR(CH₂)₂N[(CH₂)₂O(CH₂)₂OH]₂, were R is a defined above and in wone, two, or three of the nitrogens is associated with a formate,acetate or propionate group.

We believe certain of the diamine and triamine carboxylates are novelcompositions of matter. They may be made in a manner similar to that ofthe monoamines, i.e., the amine may be added first to water; then thecarboxylic acid is added slowly to control the exotherm from theneutralization between the acid and the amine. The solution becomestransparent after mixing for a few hours. Generally, the neutralizationreaction takes place in preference to any esterification possible withhydroxyl groups which may be present. Thus our invention includes as newcompositions of matter the diamine and triamine carboxylates describedherein where the R groups have at least one carbon atom. In each case, acarboxylate group is associated with at least one of the nitrogens ofthe amine group; preferably each nitrogen has an associated carboxylategroup. Stated differently, our invention includes amine carboxylatescomprising the neutralization reaction product of an amine of theformula R₂ [N[(CH₂)_(m)NR]₁₋₂]R and an acid of the formula H(CH₂)₀₋₃COOHwhere each R is independently selected from moieties of the formula—C_(n)H_(2n+1) and moieties of the formula H[O(CH₂)₁₋₄]—, each m isindependently a number from 1 to 6, and n is a number from 1 to 4.

Our invention includes the use of the compositions or formulationsdescribed above as heat exchange media. The compositions andformulations may replace virtually any commonly or commercially usedliquid heat exchange medium, such as a glycol or a mixture of glycols,or an aqueous solution of them, whether used primarily for heating orcooling. Common uses for liquid heat exchange media are in heat pumps,line heaters in gas transmission, thermal energy storage systems,cooling in various molding processes such as blow molding, and any otherprocess or device where it is desired to transfer heat from one place toanother. The solutions may be circulated (pumped, for example) toaccomplish the heat transfer or it may be conducted or convected inplace. When we use the term “heat exchange” we mean to include all suchuses, whether or not the liquid is recirculated. Any of the compositionsand solutions mentioned herein may also be used in evaporative coolingsystems, such as a cooling tower, bearing in mind the desiredconcentration should be maintained over time. As a practical matter, theheat exchange solution for any of out purposes should include at least5% by weight of the amine carboxylate, preferably 15 to 80%, and mostpreferably 25 to 65% by weight, in water, although it should beunderstood that smaller amounts, say 1% will be effective to a lesserdegree but may be useful for some purposes. Often, our heat exchangesolutions will be used in enclosed systems having heat exchange surfacesat two locations, and the objective will be to move heat energy from onelocation (heat exchange surface) to another location (a second heatexchange location), for either heating or cooling purposes at onelocation or the other and/or to achieve a desired temperature at onelocation or the other.

When our compositions are used in evaporative systems, i.e. in coolingtowers, for example, heat energy is first absorbed into a solution ofthe composition, which is circulated to a cooling tower or otherfacility where a portion of the water is evaporated, consuming heatenergy from the solution, which is then recirculated, replenished, orboth as is known in the art.

Our heat exchange solutions are compatible with potassium formate, andwe include combinations of the above described amine carboxylates withpotassium formate within our invention. Any solution of the abovedescribed amine carboxylates may include potassium formate where thepotassium formate is present in amounts up to 10:1 by weight ofpotassium formate to amine carboxylate, preferably 1:10 to 10:1. Inanother variant of our invention, where the heat exchange solutioncomprises at least 5% amine carboxylate of the type defined herein, thealkali metal formate may be present in an amount up to (from 0 or 1%)50% by weight. Where potassium formate is used, we prefer to use it inweight ratios of the amine carboxylate to potassium formate of 4:1 to1:4.

DETAILED DESCRIPTION

Certain tests and experiments have been conducted to demonstrate theinvention.

First, specific heat determinations were made on three solutions. In theTables below, the solutions are designated A, B, and C. Solution A is50% triethanolamine formate in water, Solution B is 80% triethanolamineformate, and Solution C is a combination of 40% triethanolamine formateand 35% potassium formate. Percentages are by weight of the entirecomposition.

The heated probe technique was used for thermal conductivity (lambda)measurement. Specific heat (C_(p)) values were measured using adifferential scanning calorimeter.

In the heated probe method, which may be considered as a variant of theline source method, the line source and temperature sensor are combinedin one small diameter probe. This probe is inserted into the sample andthe heater turned on for a preselected time interval. During this timeinterval, the rate of heating of the probe is measured. This heatingrate quickly becomes semi-logarithmic and from this semi-logarithmicrate the thermal conductivity of the sample is calculated. The data iscollected by a computed-based digital data acquisition system and theheating rate displayed visually. The slope of the temperature curveversus In time is chosen using cursors and the conductivity calculatedis based on this portion of the curve. The method is traceable to ASTMStandard D5334-92.

Specific heat is measured using a standard Perkin-Elmer Model DSC-2Differential Scanning Calorimeter with sapphire as the referencematerial. This instrument was calibrated using lead as the standard. TheASTM testing procedure followed was E1269. The standard and sample weresubjected to the same heat flux as a blank and the differential powersrequired to heat the sample and standard at the same rate weredetermined using the digital data acquisition system. From the masses ofthe sapphire standard and sample, the differential power, and the knownspecific heat of sapphire, the specific heat of the sample is computed.The experimental data are visually displayed as the experimentprogresses. All measured quantities are directly traceable to NISTstandards. Experimental uncertainty of the specific heat measurement is±4%; experimental uncertainty of the thermal conductivity results are±7% at room temperature and ±9% at about 70° C. The thermal conductivityresults are averages of multiple measurements.

TABLE 1 Specific Heat Results Temperature (° C.) Solution A Solution BSolution C 20 3.0020 2.4180 2.2670 24 3.0330 2.4420 2.2830 28 3.06502.4670 2.2990 32 3.0950 2.4910 2.3150 36 3.1230 2.5110 2.3270 40 3.15202.5290 2.3420 44 3.1690 2.5450 2.3490 48 3.1890 2.5620 2.3570 52 3.20902.5770 2.3640 56 3.2310 2.5940 2.3720 60 3.2540 2.6090 2.3760 64 3.27802.6260 2.3870 68 3.2980 2.6420 2.3950 72 3.3220 2.6590 2.4030 76 3.34202.6750 2.4110 80 3.3630 2.6940 2.4210

TABLE 2 Thermal Conductivity Results Conductivity Sample Temperature (°C.) (mWcm⁻¹K⁻¹) A 23.0 4.57000 66.0 4.72000 B 23.0 3.02000 67.0 3.12000C 23.0 3.55000 73.0 3.81000

Persons skilled in the art will recognize that the properties of thecompositions studied are such that they will make excellent heatexchange materials. Our invention therefore includes a method oftransferring heat energy from a first location to a second locationcomprising absorbing heat energy at the first location into an aqueoussolution comprising an amine carboxylate, the amine portion of the aminecarboxylate having an atomic ratio of N to C from 1:0 to 1:12 and thecarboxylate portion being derived from an acid of the formulaH(CH₂)₀₋₃COOH, and desorbing the heat energy from the amine carboxylatesolution at the second location. The transfer of heat energy may be forcooling or heating, may be effected by convection or conduction, and theremoval of heat energy may be accomplished through a heat transfersurface or by evaporation. The absorbtion of heat energy may also bethrough a heat transfer surface. Monoamines of the formula R₃N, diaminesof the formula R₂N(CH₂)_(m)NR₂, and triamines of the formula R₂[N[(CH₂)_(m)NR]₂]R, where each R is independently selected from moietiesof the formula C_(n)H_(2n+1) and moieties of the formula H[O(CH₂)₁₋₄]—,where n is an integer from 0 to 4, may be combined with a carboxylicmoiety of the formula derived from carboxylic acids having from 1 to 4carbon atoms, with at least one carboxylate group for each diamine ortriamine moiety, but preferably in molar ratios of carboxylate to Nof 1. As indicated above, one or more of the H[O(CH₂)₁₋₄]— groups in anyof our amine components may be further alkoxylated using alkoxy groupsof 1-4 carbon atoms, thus extending a small chain of alkoxy groups onone or more R's.

In one embodiment, an amine carboxylate comprises the reaction productof an amine of the formula R₂[N[(CH₂)_(m)NR]₁₋₂]R and an acid of theformula H(CH₂)₀₋₃COOH where each R is independently selected frommoieties of the formula —C_(n)H_(2n+1) and moieties of the formulaH[O(CH₂)₁₋₄]—, each m is independently a number from 1 to 6, and each nis a number from 1 to 4.

In one or more embodiments described herein, the amine carboxylate is inan aqueous solution.

In one or more embodiments described herein, the amine is furtheralkoxylated.

In one or more embodiments described herein, the amine is a diamine andat least one R is a moiety of the formula H[O(CH₂)₁₋₄]—.

In one or more embodiments described herein, the amine carboxylatecomprises a formate of a diamine of the formula R₂N(CH₂)₂NR₂.

In one or more embodiments described herein, the amine carboxylatecomprises a formate of an amine of the formula R₂N(CH₂)₆NR₂.

In one or more embodiments described herein, the amine is a diamine andat least one R is a moiety of the formula —C_(n)H_(2n+1).

In one or more embodiments described herein, the amine is a triamine andat least one R is a moiety of the formula H[O(CH₂)₁₋₄]—.

In one or more embodiments described herein, the amine carboxylate beinga formate of a triamine of the formula R₂N(CH₂)₆NR(CH₂)₆NR₂.

In one or more embodiments described herein, the amine carboxylate beinga formate of a triamine of the formula R₂N(CH₂)₂NR(CH₂)₂NR₂.

In one or more embodiments described herein, the amine is a triamine andat least one R is a moiety of the formula —C_(n)H_(2n+1).

In one or more embodiments described herein, the amine carboxylate formsa composition with an alkali metal formate.

In one or more embodiments described herein, the amine carboxylate formsa composition with potassium formate in a weight ratio of 4:1 to 1:4.

In one or more embodiments described herein, the alkali metal formate isin a ratio of alkali metal formate to amine carboxylate of 1:10 to 10:1.

In one or more embodiments described herein, the amine carboxylatecomprises a formate of a diamine of the formula R₂N(CH₂)₂NR₂.

In one or more embodiments described herein, the amine carboxylatecomprises a formate of an amine of the formula R₂N(CH₂)₆NR₂.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of transferring heat energy from a first location to asecond location, comprising: absorbing heat energy at said firstlocation into an aqueous solution, the solution comprising: an aminecarboxylate, the amine portion of said amine carboxylate having anatomic ratio of N to C from 1:0 to 1:12, wherein said amine carboxylatein said solution has the formula R₃NH⁺H(CH₂)₀₋₃COO^(—)where each R isindependently selected from moieties of the formula C_(n)H_(2n+1) andmoieties of the formula H[O(CH₂)₁₋₄]—, where n is an integer from 0 to 4and at least one R includes a carbon atom; and the carboxylate portionbeing derived from an acid of the formula H(CH₂)₀₋₃COOH; and desorbingsaid heat energy from said amine carboxylate solution at said secondlocation.
 2. The method of claim 1, wherein at least one of saidmoieties of the formula H[O(CH₂)₁₋₄]— is further alkoxylated to provideat least one additional alkoxy group having 1-4 carbon atoms in saidmoiety.
 3. The method of claim 1, wherein said amine portion of saidamine carboxylate satisfies the formula R₂N(CH₂)_(m)NR₂where each R isindependently selected from moieties of the formula C_(n) H_(2n+1) andmoieties of the formula H[O(CH₂)₁₋₄]—, where n is an integer from 0 to 4and m is an integer from 1 to
 6. 4. The method of claim 1, wherein saidamine portion of said amine carboxylate satisfies the formulaR₂[N[(CH₂)_(m)NR]₂]R, where each R is independently selected frommoieties of the formula C_(n)H_(2n+1) and moieties of the formulaH[O(CH₂)₁₋₄]—, where n is an integer from 0 to 4 and m is an integerfrom 1 to
 6. 5. The method of claim 1, wherein said amine carboxylate istriethanolamine formate.
 6. The method of claim 1, wherein said aminecarboxylate is present in said solution in a concentration from 15 to80% by weight.
 7. The method of claim 1, wherein said amine carboxylatesolution includes up to 50% by weight potassium formate.
 8. The methodof claim 1, wherein the amine portion of said amine carboxylate isderived from amine heads.
 9. The method of claim 1, wherein the methodis conducted in an enclosed system having heat exchange surfaces at saidfirst and second locations.
 10. The method of claim 1, wherein themethod is carried out by convection.
 11. The method of claim 1, whereinthe method is carried out by conduction.
 12. The method of claim 1,wherein said desorbing of said heat energy is carried out byevaporation.
 13. A method of transferring heat through a heat exchangesurface, comprising: absorbing said heat into a solution oftriethanolamine formate in contact with said heat exchange surface; andcirculating said solution to a second heat exchange surface.
 14. Themethod of claim 13, wherein said solution comprises 15 to 80%triethanolamine formate.
 15. The method of claim 13, wherein saidsolution includes 1% to 60% by weight alkali metal formate.
 16. Themethod of claim 15, wherein said solution includes 10% to 45% alkalimetal formate by weight.
 17. The method of claim 15, wherein said alkalimetal formate comprises potassium formate.
 18. The method of claim 1,further comprising circulating the aqueous solution from the firstlocation to the second location.
 19. A method of transferring heatenergy from a first location to a second location, comprising: absorbingheat energy at said first location into an aqueous solution, thesolution comprising: an amine carboxylate, the amine portion of saidamine carboxylate having an atomic ratio of N to C from 1:0 to 1:12,wherein said amine portion of said amine carboxylate satisfies theformula R₂ N(CH₂)_(m)NR₂ where each R is independently selected frommoieties of the formula C_(n) H_(2n+1) and moieties of the formulaH[O(CH₂)₁₋₄]—, where n is an integer from 0 to 4 and m is an integerfrom 1 to 6; and the carboxylate portion being derived from an acid ofthe formula H(CH₂)₀₋₃COOH; and desorbing said heat energy from saidamine carboxylate solution at said second location.
 20. The method ofclaim 1, wherein the solution comprises an alkali metal formate.
 21. Themethod of claim 1, wherein the atomic ratio of nitrogen to carbon is1:1.